Minimally invasive networked surgical system and method

ABSTRACT

A system for performing non-invasive networked medical procedures including a number of in vivo medical devices, a communication path between at least two of the devices, an ex vivo control unit to control the behavior of the devices, and a wireless communication path between the control unit and at least one of the devices. An associated method for performing non-invasive networked medical procedures is also provided. Further included is a simulation method that utilizes accurate electromagnetic field simulations, using a software based test bench, to determine the maximum allowable transmitted power levels from in vivo devices to achieve a required bit error rates (BER) at an in vivo or ex vivo node (receiver) while maintaining the specific absorption rate (SAR) under a required threshold.

CROSS REFERENCE TO RELATED APPLICATIONS

This nonprovisional application is a continuation of and claims priorityto U.S. Provisional Application No. 61/912,321, entitled “MinimallyInvasive Networked Surgical System and Method”, filed Dec. 5, 2013 bythe same inventors, the entirety of which is incorporated herein byreference.

FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

This invention was made with Government support under Grant No.IIP-1217306 awarded by the National Science Foundation. The governmenthas certain rights in the invention.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates, generally, to a system and method device forminimally invasive surgical procedures. More specifically, it relates toa network of various in vivo medical devices.

2. Brief Description of the Prior Art

As minimally invasive surgical (MIS) procedures become increasingsophisticated, new functions will be needed to realize successfulsurgical outcomes. For example, conventional laparoscopy places a limiton the number of devices that can be inserted in the body. In addition,these devices have limited positioning capabilities and may compete orinterfere with the preferred motion or position of another instrument.

Devices and methods for performing in vivo imaging of passages orcavities within a body are known in the art, and there areself-propelled devices known in the art. However, these conventionaltechnologies use a single device (e.g. a camera pill), which aredifficult to inject into the body and properly position and navigate dueto their size. Having a single device also limits the ability of thesurgeon to perform multiple tasks in a single session, or view theprogress of the surgical procedure from the most advantageous angle.

Generally, wireless communication for biomedical applications is aresearch topic that has seen a tremendous increase in attention inrecent years (C. Castro, A. Alqassis, S. Smith, T. Ketterl, Y. Sun, S.Ross, A. Rosemurgy, P. Savage, and R. Gitlin, “A Wireless Robot forNetworked Laparoscopy,” IEEE Transactions on Biomedical Engineering, pp.930-936, April 2013; A. Alqassis, T. Ketterl, C. Castro, R. Gitlin, S.Ross, Y. Sun, and A. Rosemurgy, “MARVEL IN VIVO WIRELESS VIDEO SYSTEM,”Technology & Innovation, vol. 14, no. 3, pp. 329-340, March 2012; G. E.Arrobo and R. D. Gitlin, “New approaches to reliable wireless body areanetworks,” in IEEE International Conference on Microwaves,Communications, Antennas and Electronics Systems (COMCAS 2011), TelAviv, Israel, 2011, pp. 2-6; M. Chen, S. Gonzalez, A. Vasilakos, H Cao,and V. C. M. Leung, “Body Area Networks: A Survey,” Mobile Networks andApplications, vol. 16, pp. 171-193, August 2010; M. A. Hanson, H. C.Powell, A. T. Barth, K. Ringgenberg, B. H. Calhoun, J. H Aylor, and J.Lach, “Body Area Sensor Networks: Challenges and Opportunities,”Computer DOI—10.1109/MC.2009.5, vol. 42, no. 1, pp. 58-65, 2009; HuasongCao, V. Leung, C. Chow, and H Chan, “Enabling technologies for wirelessbody area networks: A survey and outlook,” Communications Magazine,IEEE, vol. 47, no. 12, pp. 84-93, 2009).

Implanted sensors and actuators for medical applications have thepotential of being critical components in advanced health care deliveryby reducing the invasiveness of a number of medical procedures. Suchapplications include, but are not limited to, internal health monitoringand drug administration (E. Piel, A. Gonzalez-Sanchez, H. Gross, and A.J. C. van Gemund, “Spectrum-Based Health Monitoring for Self-AdaptiveSystems,” in Self Adaptive and Self-Organizing Systems (SASO), 2011Fifth IEEE International Conference on, 2011, pp. 99-108; E. Y. Chow, B.Beier, Y. Ouyang, W. J. Chappell, and P. P. Irazoqui, “High frequencytranscutaneous transmission using stents configured as a dipole radiatorfor cardiovascular implantable devices,” in IEEE MTT-S InternationalMicrowave Symposium Digest, 2009, pp. 1317-1320).

Current medical sensors use dedicated systems (dedicated system for eachdevice) for wireless communications, data processing, and backenddatabases. These systems rely on low data rate communications andbest-effort processing of aggregate data. However, one must considerspecific absorption rate (SAR) levels and bit-error-rate (BER) whenutilizing this technique.

SAR levels of radio frequency (RF) radiation produced by cellular phoneactivity near the human head have already been extensively investigated(M. H. Mat, M. F. B. A. Malek, A. Omar, M. S. Zulkefli, and S. H.Ronald, “Analysis of the correlation between antenna gain and SAR Levelsinside the human head model at 900 MHz.” in Asia-Pacific Symposium onElectromagnetic Compatibility (APEMC), 2012, pp. 513-516; M. Ahmed,“Investigating Radiation Hazard and Safety Aspects of Handheld Mobile,”in Third international Conference on Mobile Ubiquitous Computing,Systems, Services and Technologies, 2009, pp. 1-9; C. Lazarescu, 1.Nica, and V. David, “SAR in human head due to mobile phone exposure,” inE-Health and Bioengineering Conference (EHB), 2011, 2011, pp. 1-4). SAReffects near other parts of the human body, such as in body areanetworks (BAN) applications (IEEE P802.15 Working Group for WirelessPersonal Area Networks (WPANs), “Channel Model for Body Area Network(BAN).”) have also seen increased attention (T. Koike-Akino, “SARAnalysis in Dispersive Tissues for In vivo UWB Body Area Networks,” inGlobal Telecommunications Conference, 2009. GLOBECOM 2009. IEEE, 2009,pp. 1-6).

However, research in SAR levels produced by in vivo devices has so farbeen very limited (S. Aoyama, D. Anzai, and J. Wang, “SAR evaluationbased on required BER performance for 400 MHz implant BANs,” inAsia-Pacific Symposium on Electromagnetic Compatibility, 2012, pp.365-368). Although, in Aoyama et al., the authors provided results forspecific absorption rate SAR and BER evaluation for implant BAN'soperating at the 400 MHz ISM band. Due to an increasing need to providehigh data rate in in vivo communications, however, it is essential toevaluate the SAR under BER requirements at higher frequencies. Suchresults will give the system designer guidance about whether a relaynetwork will be needed to attain reliable communications through theextremely lossy and dispersive in vivo channel (T. P. Ketterl, G. E.Arrobo, A Sahin, T. J. Tillman, H Arslan, and R. D. Gitlin, “In vivowireless communication channels,” in IEEE 13^(th) Annual Wireless andMicrowave Technology Conference, 2012, pp. 1-3).

Accordingly, what is needed is unified system or method for controllinga networked plurality of in vivo medical devices in the body of asubject, while reducing clutter and improving the quality andreliability of communications. However, in view of the art considered asa whole at the time the present invention was made, it was not obviousto those of ordinary skill in the field of this invention how theshortcomings of the prior art could be overcome.

While certain aspects of conventional technologies have been discussedto facilitate disclosure of the invention, Applicants in no way disclaimthese technical aspects, and it is contemplated that the claimedinvention may encompass one or more of the conventional technicalaspects discussed herein.

The present invention may address one or more of the problems anddeficiencies of the prior art discussed above. However, it iscontemplated that the invention may prove useful in addressing otherproblems and deficiencies in a number of technical areas. Therefore, theclaimed invention should not necessarily be construed as limited toaddressing any of the particular problems or deficiencies discussedherein.

In this specification, where a document, act or item of knowledge isreferred to or discussed, this reference or discussion is not anadmission that the document, act or item of knowledge or any combinationthereof was at the priority date, publicly available, known to thepublic, part of common general knowledge, or otherwise constitutes priorart under the applicable statutory provisions; or is known to berelevant to an attempt to solve any problem with which thisspecification is concerned.

BRIEF SUMMARY OF THE INVENTION

The long-standing but heretofore unfulfilled need for an improvedwireless communication between in vivo sensors/actuators and ex vivotransceivers for performing minimally invasive networked surgicalprocedures is now met by a new, useful, and nonobvious invention.

The present invention includes a system and associated method forperforming minimally invasive, networked medical procedures. The systemincludes a number of in vivo medical devices, such as imaging devices,sensors and actuators, power sources, cutting tools (physical, optical,ultrasound, etc.), and other ancillary devices, and a communication pathbetween at least two of the in vivo medical devices. The system furtherincludes an ex vivo control unit to control the behavior of the in vivomedical devices and a wireless communication path between the controlunit and at least one of the in vivo medical devices. The system mayfurther include a second wireless communication path between at leastone of the in vivo medical devices and an ex vivo system.

The communications and control units may be combined into a single unitand their communications paths may be shared. The in vivo medicaldevices may be electronically addressable and electronicallycontrollable and form a distributed wireless network whose capabilitiesexceed that of individual devices. The in vivo medical devices may alsobe magnetically controllable. There also may be a number of wirelesscommunication paths between the control unit and each of the in vivomedical devices. These wireless communications links, or additionalwireless links, also provide a two-way communication path for thein-vivo devices to communicate a variety of information with externalsystems.

The method of performing networked medical procedures includes providinga number of in vivo medical devices and a communication between at leasttwo of the in vivo medical devices. The method further includesproviding an ex vivo control unit to control the behavior of the in vivomedical devices and providing a wireless communication path between thecontrol unit and at least one of the in vivo medical devices. The methodalso includes controlling the behavior of the in vivo medical devicesfrom outside the body using the wireless communication path between thecontrol unit and the at least one of the in vivo medical devices. Themethod may further include providing a second wireless communicationpath between at least one of the in vivo medical devices and an ex vivosystem. The second wireless communication path may be a duplex wirelesscommunication path.

Controlling the behavior of the in vivo medical devices from outside thebody using the wireless communication path between the control unit andat least one of the in vivo medical devices may include generating acontrol signal at the control unit and transmitting the control signalover the wireless communication path to a first in vivo medical device.Controlling the behavior of the in vivo medical devices from outside thebody may also include receiving the control signal at the first in vivomedical device, generating a second control signal at the first in vivomedical device, and transmitting the second control signal over thecommunication path between the first in vivo medical device and a secondin vivo medical device to the second in vivo medical device.

These and other important objects, advantages, and features of theinvention will become clear as this disclosure proceeds.

The invention accordingly comprises the features of construction,combination of elements, and arrangement of parts that will beexemplified in the disclosure set forth hereinafter and the scope of theinvention will be indicated in the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

For a fuller understanding of the invention, reference should be made tothe following detailed description, taken in connection with theaccompanying drawings, in which:

FIG. 1 is a general diagram of a plurality of in vivo medical devices,which are networked together and controlled wirelessly via a wirelessaccess point located outside the body, in accordance with an embodimentof the present invention.

FIG. 2 is a diagram of a plurality of exemplary in vivo medical devices,which are networked together and controlled wirelessly by a control unitlocated outside the body, in accordance with an embodiment of thepresent invention.

FIG. 3 is a block diagram of a system level simulation showing directlinks to the HFSS in vivo channel model.

FIG. 4A is truncated HFSS human body model used to derive SAR levels onthe channel model.

FIG. 4B is a cross section of the model of FIG. 4A showing receive andtransmit antenna locations.

FIG. 5A is a front cross-sectional view of the total SAR generated at2.412 GHz inside the abdomen at a transmit power of 0.412 mW.

FIG. 5B is a side cross-sectional view of the total SAR generated at2.412 GHz inside the abdomen at a transmit power of 0.412 mW.

FIG. 6 is a graphical illustration showing BER performance as a functionof distance for different data rates at the threshold power (0.412 mW).

FIG. 7 is a graphical illustration showing achievable distance, as afunction of bit rate, between in vivo and external antennas for a BER of10⁻⁶.

FIG. 8 is a human body model showing the hub (external node), bodysurface nodes (devices), and implanted nodes (devices), and therelationships therebetween.

FIG. 9 is a human body schematic showing the destination/hub/gateway(external node), body surface nodes, and implanted nodes, and therelationships therebetween.

FIG. 10 is a flow diagram showing exemplary security measures used inWBANs.

FIG. 11 is a diagram showing PHY human body communications.

FIG. 12 is graphical illustration of signal loss for in vivo attenuationversus free space loss.

FIG. 13A is a graphical illustration of results of a vivarium experimentusing a MARVEL CM showing differences in signal strength between the invivo and external measurements.

FIG. 13B is a graphical illustration showing normalized channel impulseresponse over time for the human body for free space and scatteredenvironments.

FIG. 14A is a graphical illustration of path loss as a function ofposition for the human body with the transmitter at (0,0) and measuredat a height of 1.1 m. The attenuation at any point (x,y) is[(P_(x))²+(P_(y))²]^(1/2).

FIG. 14B is a graphical illustration of channel impulse response for thehuman body for different locations of the receiver.

FIG. 15A is schematic showing multiple transmit and receive antennas(MIMO).

FIG. 15B is a graphical illustration showing capacity increase with anincrease in number of channels without increasing total power.

FIG. 16 is a schematic showing cooperative MIMO in vivo.

FIG. 17 is a schematic showing network coding.

FIG. 18 is a schematic showing a configuration of the MARVEL system.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

In the following detailed description of the preferred embodiments,reference is made to the accompanying drawings, which form a parthereof, and within which are shown by way of illustration specificembodiments by which the invention may be practiced. It is to beunderstood that other embodiments may be utilized and structural changesmay be made without departing from the scope of the invention.

The present invention includes a system and associated method forperforming non-invasive medical procedures. The system includes a numberof networked devices for in vivo medical applications, whereby thesystem creates a wireless network of cyber-physical in vivo devices thatenhances and enables innovative non-invasive and MIS surgical and otherprocedures. Typical applications include, but are not limited to,procedures in the gastrointestinal tract of a human being. The systemand method allow for the performance of complex and time-consumingsurgeries to be minimally invasive and in some cases with only local orno anesthesia. This increases the safety of the surgery and minimizespatient anxiety. The current invention can further provide new(asymmetric) communications and multihop networking paradigms fordevices to achieve reliable, high-throughput and near zero latencyintra-body wireless communications and networking. This system iscapable of coping with the complexity of an in vivo multipath RFchannel.

The invention includes a plurality of in vivo medical devices of thesame or different types, such as imaging devices, sensors, powersources, collectors, and “cutting” tools (physical, optical, ultrasound,lasers, etc.). There also may be multiples of the same type of device.For example, multiple batteries may be used so that the devices do notprematurely run out of power.

The devices are controlled by one or more external (ex vivo) controlunits, such as an expert system. The invention may include otherexternal (ex vivo) systems in addition to the control unit. Examples ofsuch an external system include a server and an external display systemfor displaying images from an in vivo video camera. The invention mayfurther include one or more external (ex vivo) communication units, suchas an external wireless access point, which transmit data between the invivo medical devices and the one or more external control units or otherexternal systems.

Such ex vivo control units may be implemented on smartphones or otherdevices, such has those capable of implementing a 32-bit processorarchitecture and having low power consumption with high energy densitybattery. However, any device is contemplated for the purpose of thesecommunications.

The invention may also include one or more communication paths betweenone or more of the in vivo medical devices and the external system(s).These communication paths may carry control signals or any other type ofcommunication required by the system. The communication path may eitherbe a separate communications link with dedicated resources (e.g.separate frequency, time slot, or code, for each “path”) or anaddressable logical link in a shared medium (such as a packet network).Each communication path may be uni- or bi-directional depending on theneeds of the system. For example, an in vivo video camera may have adedicated communication path between it and an external control anddisplay system. The control signal would be sent from the externalsystem to the video camera via the communication path and the camerawould send images to the external system via the same communicationpath. Alternatively, there may be more than one communication pathbetween two devices—one carrying control signals and another forcommunication.

The invention may also include one or more communication paths betweenthe in vivo medical devices. These communication paths may carry controlsignals or any other type of communication required by the system. Thecommunication paths may also relay information received by one in vivomedical device from an external system to another in vivo medicaldevice. Each communication path may be uni- or bi-directional dependingon the needs of the system.

Each of the devices may be externally electronically addressable. Eachdevice may be externally controllable (e.g., via wireless, magnetic, orother means). Each device may perform a required task in response toexternally generated control signals. The device may be positioned inresponse to the control commands. Movement of the devices may beaccomplished in a variety of ways including mini motors and thrusters,as well as the use of magnets. The devices may have means of acquiringposition or other information (e.g., a GPS). The devices may be capableof originating communications with the external systems or with other invivo devices. These communications may, for example, communicate theinformation acquired by the device and/or the status or condition of thedevice.

The devices may assume a hierarchical, mesh, tree, ad-hoc, or otherarchitecture that is appropriate for the application.

Exemplary implantable device applications may include, withoutlimitation, imaging applications (implanted devices with camera andlight source for transmission of image data; e.g., camera pill,laparoscopic cameras, etc.), sensors (implanted devices that can testfor biological conditions or symptoms and transmit data to externalreceivers or regulate other medical devices or actuators; e.g.,implanted RFID sensors, glucose monitor, EKG sensors, etc.), andactuators (implanted devices that perform specific actions in responseto internal programming or an external stimulus; e.g., neuro-stimulator,drug delivery, insulin pumps, etc.).

A generalized example of the present invention is shown in FIG. 1. Inthis example, plurality of in vivo medical devices 110A-110D arenetworked together and controlled wirelessly via wireless access point105 located outside body cavity 100 and gateway on the body (not shownin this figure, but seen in FIG. 9, where the wireless access point iscommunicatively coupled with the gateway, and the gateway iscommunicatively coupled to in vivo medical devices 110A-110D).

Another example is shown in FIG. 2. Here, the in vivo medical devicesinclude cutting tool 210A with positioning device 215A, battery 210Bwith positioning device 215B, camera 210C with positioning device 215C,light 210D with positioning device 215D, battery 210E with magnet 215E,sensor 210F with magnet 215F, and monitor 210G with positioning device215G. Positioning devices include any device that provides movement tothe respective in vivo medical device, such as mini-motors or thrusters.In addition, external magnet 212 may be used in conjunction with magnet215E or 215F to move battery 210E or sensor 210F, respectively.

In vivo medical devices 210A-210G may be connected to one or more ofeach other via a wired or wireless connection. For example, in FIG. 2,camera 210C has a wired connection with battery 215B and a wirelessconnection with light 210D. Further, any number of in vivo medicaldevices 210A-210G may be wirelessly connected to an external controlunit, here computer 205. In this example, four in vivo medical devicesare wirelessly connected to computer 205—cutting tool 210A, camera 210C,light 210D, and monitor 210G.

High Data Rate Communication

In carrying out certain embodiments of the current invention, high datarate communication systems (e.g., in point-to-point systems, networks,etc.) can be developed between implanted and external receivers for useduring minimally invasive surgical procedures. For example, oneapplication that may require high data transmission capabilities is highdefinition (HD) video from the in vivo camera modules.

To reliably transmit a high data rate signal through the in vivo channelrequires a given signal-to-noise ratio (SNR) and appropriate forwarderror control. One method to monitor the performance of a digitalcommunication system is to measure the BER of the communication. A lowBER is needed for high communication performance which depends on thetransmission power to obtain the required SNR. However, since data isbeing transmitted through or near the human body, the signal levels arelimited to the safety guidelines set by the Federal CommunicationsCommission (FCC). The method described herein allows the communicationsystem designer to simultaneously monitor the BER of the system and theresulting SAR levels of the in vivo transmitter.

An example of a type of network that can be used is a wide body areanetwork, which can transmit at low power to protect patients againstharmful health effects associated with the RF emissions as well as toextend the battery lifetime of the node (device). SAR is the rate atwhich the RF energy is absorbed by a body volume or mass and has unitsof watts per kilogram (W/Kg). This sets a limit on the transmittedpower. The SAR limit is frequency dependent, since it depends on theconductivity of the material, which changes with frequency in humanorgans/tissues. Due to this limitation on the specific absorption rate,it is not possible to increase the transmission power beyond a certainlevel to overcome transmission errors. By networking the in vivo nodesvia relay nodes, it is possible to transmit the in vivo sensors'information to external nodes while keeping the SAR within allowedlimits.

The methodology described herein that utilizes accurate electromagneticfield simulations to study the maximum allowable transmitted powerlevels from a network of in vivo devices to achieve a required BER atthe external or in vivo node (receiver) while maintaining the SAR undera required threshold. The BER of the communication can be calculatedusing the derived power threshold for a given modulation scheme. Theseresults can be used to optimize the transmitted power levels whileassuring that the safety guidelines, given by the FCC, in terms of theresulting SAR of transmitters placed in any location inside the humanbody are met. A software-based test bench is utilized to facilitate theimplementation of field solver solutions directly into systemsimulations. This test bench allows the system designer to easilymonitor the performance of the communication while, at the same time,observe the SAR levels using highly accurate in vivo models.

In the following experimentation, SAR levels and communication BER werecalculated using the software-based test bench, where the systemdesigner can monitor the performance of the communication, whilesimultaneously observing the SAR levels in highly accurate in vivoenvironments. The goal of the experimentation is to study the maximumallowable transmitted power levels from in vivo devices to achieve arequired BER at the ex vivo node (receiver) while maintaining the SARunder a required threshold

The dynamic link capabilities between the ANSYS Designer, which is acomplete RF circuit and systems simulation tool, and ANSYS HFSS, a highfrequency numerical electromagnetic field simulator, were utilized,along with a highly accurate human body model in HFSS, to create thetest bench.

Simulation tests were run to determine any limitations that might beexperienced by the networked in vivo medical devices in a human body.The tests utilized accurate electromagnetic field simulations to studythe maximum allowable transmitted power levels from in vivo devices toachieve a required BER at the external node (receiver), whilemaintaining the SAR under a required threshold. The BER of thecommunication can be calculated using the derived power threshold for agiven modulation scheme. These results can be used to optimize thetransmitted power levels while assuring that the safety guidelines—interms of the resulting SAR of transmitters placed in any location insidethe human body—are met. To evaluate SAR and BER, a software-based testbench that allows an easy way to implement field solver solutionsdirectly into system simulations was developed. To demonstrate thesoftware-based test bench design, a complete OFDM-based communication(IEEE 802.11g) for the in vivo environment was simulated. Results showedthat for cases when noise levels increased or the BER became morestringent, a relay network or the use of multiple receiver antennas,such as in a MIMO system, would be desired to achieve high data ratecommunication.

SAR and BER

The interaction of electromagnetic fields with human body tissues causelocalized tissue heating and damage in the vicinity of radiating sourcesat unsafe power levels. To restrict the amount of radiation that theliving tissue can be subjected to, strict guidelines were set by theFCC. The SAR, a measurement of how much power is absorbed per unit massof a conductive material, is defined as follows (“C95.1-200S: IEEEStandard for Safety Levels With Respect to Human Exposure to RadioFrequency Electromagnetic Fields, 3 kHz to 300 GHz,” 2006):SAR=σ|E| ²/ρwhere σ is the electrical conductivity of the material, E is the RMSmagnitude of the electric field at a given point, and ρ is the massdensity of the material.

The FCC recommended that the SAR level is given for localized areas overany one (1) gram of tissue and for values averaged over the whole humanbody, also known as local SAR and average SAR, respectively. The limitfor the local SAR and average SAR are 1.6 W/kg and 0.08 W/kg,respectively. Since the communication system is limited by how muchwireless power can be transmitted near and through the human body,emphasis is placed on optimizing the system performance to ensure thatthe required BER for reliable wireless in vivo communication is met.

The test bench uses a propagation channel model derived directly inHFSS, meaning that the BER values in each simulation are dependent onthe specific antenna performance and placement. Therefore, this testbench allows the system designer not only to decide on optimum systemarchitecture and data rates for reliable communication, but also theflexibility of using different antenna architectures, while alsooptimizing the antenna designs and placement. With this test bench, invivo devices can be arbitrarily placed in any part of the human body andeasily characterized for SAR levels and BER.

Test Bench

The test bench presented was implemented on ANSYS Designer 8.0 and ANSYSHFSS 15.0. ANSYS Designer allows for design of complete communicationsystems, both at the system and circuit levels. For digital systems,link quality measurements, such as BER constellation diagrams and eyediagrams, among others, are easily simulated in ANSYS Designer. ANSYSalso provides a complete human body model of a detailed adult male withover 300 muscles, organs, and bones with a geometrical accuracy of one(1) mm with realistic frequency-dependent material parameters(conductivity and permittivity) from 20 Hz to 20 GHz. This model is usedin HFSS to derive the complete electromagnetic fields produced by anarbitrary radiation source, from which other characteristics, such asscattering parameters and SAR levels, can be directly obtained.

The simulation was performed as follows:

-   -   1. The transmit and receive antennas are placed into the HFSS        design with the human body model.    -   2. Field solutions and S-parameter calculations are derived in        HFSS over the desired frequency band (and bandwidth).    -   3. The maximum local SAR levels from the transmit antenna are        evaluated in HFSS as a function of frequency. From these data,        the maximum allowable power levels can be derived and used in        the Designer system simulations.    -   4. The communication system is set up in Designer.    -   5. The wireless channel model, derived in the previous HFSS        simulation, is used in the Designer system simulations through        the direct link between HFSS and Designer.    -   6. A BER calculation is performed in Designer at various noise        levels, using the required power levels (derived in step 3).

Simulation Example

To evaluate the BER performance of in vivo systems, an OFDM-based(802.11g) wireless transceiver model operating at 2.4 GHz was set upwith varying transmission and noise power levels, and bit rates inDesigner. The OFDM transceiver was simulated using the field simulationsobtained from HFSS simulation with the ANSYS human body model from whichthe maximum allowable local SAR was found, along with the path loss as afunction external receiver antenna location. The threshold power derivedfrom these SAR levels was then used in the system simulation tocalculate the corresponding BER as a function of external antennalocation for data rates of 9, 18, and 36 Mbps. The system block diagramis shown in FIG. 3.

For simplicity in this proof-of-concept demonstration, monopole antennaswere used in the HFSS simulation, which have been optimized to operateat the design frequency. The in vivo antenna is placed inside theabdomen to simulate placement of transceivers in laparoscopic andintestinal medical applications, and the er vivo antenna is placed at adistance between one (1) and ten (10) cm in front of the abdomen at thesame planar height as the in vivo antenna to obtain the path loss as afunction of distance (the in vivo antenna is located 7.8 cm from theabdominal wall). The 3-D model used in HFSS showing the antennalocations can be seen in FIGS. 4A-4B.

For this example, only the local SAR values were calculated since theinduced SAR levels are mainly localized near the transmitting antenna(M. H. Mat, M. F. B. A. Malek, A. Omar, M. S. Zulkefli, and S. H.Ronald, “Analysis of the correlation between antenna gain and SAR Levelsinside the human head model at 900 MHz,” in Asia-Pacific Symposium onElectromagnetic Compatibility (APEMC), 2012, pp. 513-516). HFSScalculates the local SAR levels through the whole body and the testbench provides the maximum value with respect to the input powerspecified in the system simulation.

Table 1 shows the calculated SAR levels over the required bandwidth forthe 2.4125 GHz 802.11g carrier frequency band with one (1) mW oftransmit power. Since the SAR scales linearly with power, the maximumallowable transmit power can be calculated, such as 0.412 mW of peakpower in this example. The new SAR levels due to the calculatedthreshold power are also shown in Table 1.

TABLE 1 Calculated SAR levels for different frequencies in the 2.4 GHzband at 1 mW and at the threshold power. SAR @ Threshold Frequency SAR @1.0 mW Power (0.412 mW) GHz W/kg W/kg 2.402 4.34 1.585 2.412 3.25 1.5627.422 3.29 1.539

A visual plot of the total SAR levels is shown in FIGS. 5A-5B. FIGS.5A-5B show the total SAR over a cross-sectional cut when viewed from thefront and side, respectively. From these SAR plots, the location of themaximum total SAR generated at 2.412 GHz inside the abdomen at atransmit power of 0.412 mW occurs at points closest to the in vivomonopole antenna. It can also be observed that the SAR reduces veryrapidly away from the antenna, which is to be expected since theelectric field attenuates with distance in a conductive medium.Achievable distance, as a function of bit rate, between in vivo andexternal antennas for a BER of 10⁻⁶ can be seen.

The average SAR was also calculated using the threshold power levelscalculated from the maximum local SAR. To calculate the average SAR, aone (1) cm² averaging box was positioned at the location of the maximumSAR. The maximum average SAR was determined in this averaging box andfound to be 0.0133 W/kg. This value is within the guideline level of0.08 W/kg set for the average SAR in the human body.

The maximum allowable power derived in the HFSS simulation was then usedin the OFDM system simulation in Designer. Using a noise level of −101dBm, the thermal noise with 20 MHz BW, FIG. 6 shows the BER as afunction of distance between the external and in vivo antenna with addedGaussian noise for three data rates that follow the 802.11g standard forcoding rates and modulation types: 9, 18, and 36 Mbps. In the case whentransmitting data at 36 Mbps, the external antenna should be placedwithin 1.4 cm from the body to achieve a minimum BER of 10⁻³.

The maximum achievable distance between transmit and receive antennaswas also calculated as a function of the given data rates in the IEEE802.11g, shown in FIG. 7. The calculation was performed using themaximum threshold power levels of 0.412 mW and a −101 dBm noise level ata BER of 10⁻⁶.

From the data found in this study, it is evident that there arelimitations when transmitting at high frequencies from in vivo devicesto ex vivo transceivers while still achieving reliable datatransmission, since the maximum transmit power is restricted by SARsafety guidelines. When operating under low noise conditions withmoderate BER requirements (10⁻³), reliable data transmission to anexternal receiver can be achieved when located very close to the body.For cases when noise levels increase or the BER becomes more stringent,a relay network or the use of multiple receive antennas, such as in aSIMO system, may be necessarily to achieve high data rates.

The maximum SAR levels occur at points closest to the transmit antenna;thus, by placing the transmitter further from organs, the power levelscould possibly be increased to obtain higher signal levels at theexternal receiver. In this example, the transmitter was located veryclose to the small intestine and the spine. Therefore higher BER shouldbe achievable with proper placement of the in vivo transmitter (furthestpossible distance from organs and tissues).

The test bench can be used by a person having ordinary skill in the artto further optimize the system design (e.g. using asymmetrical OFDM,MIMO transceivers, etc.) as well as the antenna architectures andlocation to meet BER requirements while always staying within theradiation safety guidelines.

Area Networks

Examples of networks that may be utilized to carry out certainembodiments of the current invention include, but are not limited to, awireless local area network (WLAN), a wireless personal area network(WPAN), and a wireless body area network (WBAN). WLANs links two or moredevices using a wireless distribution method, and usually provides aconnection through an access point to the Internet. WPANs is acommunication network for interconnecting devices centered around anindividual person's workspace. Standards currently in use can be seen inTable 1:

TABLE 1 Standards of area networks currently in use. Max Data Band- RateRange width Comm. Standard (Mbps) (m) (MHz) Technology IEEE 802.11A/B/G/N 54 - A/G 50-100 20 OFDM WiFi 600 - N 40 Bluetooth v4.0(Bluetooth 0.200 10-50  2 DSSS Low Energy) IEEE 802.15.4 (Zigbee) 0.25010-100 5 DSSS IEEE 802.15.6 (WBAN) 15.6 <5 499.2 Impulse Radio (IR),CP-BFSK

A WBAN is a collection of low-power, intelligent devices, such assensors or actuators, which are embedded, on-body, or in close proximityto the human body and are wirelessly interconnected. An exemplaryillustration can be seen in FIG. 8, where an external link originatesfrom the destination/hub and travels to the body surface nodes (glucosemonitor and relay), where the node is a device. Subsequently, in vivobody surface links originate from the glucose monitor and relay andtravel to the implanted nodes (pacemaker and video capsule,respectively). Each WBAN can have one (1) hub and up to 64 nodes.

WBANs are receiving considerable attention because they can provideubiquitous real-time monitoring, often without restricting the person'sregular activities. A WBAN is a network formed by low power andlimited-energy networked nodes that monitor vital human signs and arelocated in, on or around the human body. WBANs have certain operatingcharacteristics and requirements, such as limited transmission andprocessing power (size, battery, and transmit power (SAR) limitations toavoid hazardous RF radiation to the human body, as well as to extend thenode's battery lifetime), minimal or negligible latency, especially forreal-time applications (in vivo video monitoring), and operation in ahighly lossy, dispersive, and time varying (due to the movement ofinternal fluids such blood) RF channel. An illustration of in vivowireless communications and networking using WBAN can be seen in FIG. 9.

WBANs must satisfy stringent technical requirements, especially when thenetwork is monitoring life-saving related signals such as indicators ofa heart attack. A WBAN should be extremely reliable by avoiding singlepoints of failure and providing self-healing capabilities if nodes orlinks are not operating properly, should have low power transmission toextend the network lifetime and preclude any harmful effects in thehuman body, and should maximize throughput over a lossy, dispersive, anddynamic channel. A frequent constraint is that it is often neitherpossible nor desirable to retransmit the sensor data.

A typical WBAN architecture can include a common MAC layer and three (3)physical layers. The common MAC layer generally has a MAC header, MACframe body (0-255 octets) and FCS (2 octets). The MAC header can haveseven (7) octets, including frame control (protocol version, ACK policy,security level, frame type, sequence number, etc.) being four (4)octets, recipient ID being one (1) octet, sender ID being one (1) octet,and BAN ID being one (1) octet. The three (3) physical layers can be PHYnarrowband, PHY ultra wideband, and PHY human body communications (usingskin as a conductor).

Regarding security, WBAN provides a self-contained, low-overhead, butstrong security solution between nodes and hub. There is a master keygeneration through master key (MK) pre-shared association,unauthenticated association, public key hidden association,password-authenticated association, and display-authenticatedassociation. There can be a simple two-way handshake for MK pre-sharedassociation with elliptic curve cryptography (ECC) based for keyagreement.

A temporal key can also be created or distributed, including pairwisetemporal key (PTK) creation for unicast protection and group temporalkey (GTK) distribution for multicast/broadcast protection. Dataauthentication/encryption (e.g., AES-128 CCM) can also be used, allowingfor replay prevention and low security overhead. FIG. 10 illustratesWBAN security.

The WBAN MAC layer may include prioritization of supported services, forexample non-medical services, mixed medical and non-medical services,general health services, and highest priority medical services. Anexample priority mapping can be seen in Table 2.

TABLE 2 WBAN MAC layer priority map. Priority User priority Trafficdesignation Frame type Lowest 0 Background (BK) Data 1 Best effort (BE)Data 2 Excellent effort (EE) Data 3 Video (VI) Data 4 Voice (VO) Data 5Medical data or Data or network control management 6 High prioritymedical Data or data or network control management Highest 7 Emergencyor medical Data event report

The PHY-dependent MAC sublayer, which uses standard wireless MACs, caninclude narrowband PHY (CSMA/CA), UWB PHY (CSMA/CA or Slotted Aloha,Hybrid ARQ (type 11)), and HBC PHY (Slotted Aloha).

The PHY narrowband can include the following:

-   -   Channel coding [BCH (n=63, k=51)]→Add pad bits→Spreader→Bit        interleaver→Scrambler→Symbol mapper

TABLE 3 PHY Narrowband. Frequency Band Information Data (MHz) ModulationRate (kbps) Support 402-405 π/2-DBPSK 75.9 Mandatory (BW: 300 KHz)π/2-DBPSK 151.8 Mandatory Implantable π/4-DBPSK 303.6 Mandatoryπ/8-DBPSK 455.4 Optional 420-450 GMSK 75.9 Mandatory (BW: 320 KHz) GMSK151.8 Mandatory GMSK 187.5 Optional 863-870 π/2-DBPSK 101.2 Mandatory902-928 π/2-DBPSK 202.4 Mandatory 950-958 π/4-DBPSK 404.8 Mandatory (BW:400 KHz) π/8-DBPSK 607.1 Optional 2360-2400 π/2-DBPSK 121.4 Mandatory2400-2483.5 π/2-DBPSK 242.9 Mandatory (BW: 1 MHz) π/2-DBPSK 485.7Mandatory π/4-DBPSK 971.4 Mandatory

The ultra-wideband (UWB) PHY specification is designed to offer robustperformance for BANs and provide a large scope for implementationopportunities for high performance, robustness, low complexity, andultra-low power operation. There are two PHY UWB technologies defined inthe standard: Impulse radio (IR-UWB) and wideband FM (FM-UWB). IR-UWB isbased on transmission of either a single pulse (new paradigm) or a burstof pulses (legacy) per information symbol. FM-UWB combines continuousphase binary FSK (CP-BFSK) modulation with wideband FM. The UWB PHYprovides three levels of functionality: (1) Activation and deactivationof the radio transceivers. (2) The UWB PHY may provide clear channelassessment (CCA) indication to the MAC in order to verify activity inthe wireless medium. (3) The PLCP constructs the PHY layer protocol dataunit (PPDU) by concatenating the synchronization header (SHR), physicallayer header (PHR) and physical layer service data unit (PSDU). Thetransmit order proceeds in the order of SHR, PHR, and PSDU.

TABLE 4 Ultra Wideband (UWB). Channel Center frequency Bandwidth ChannelBand group number (MHz) (MHz) attribute Low band 1 3494.4 499.2 Optional2 3993.6 499.2 Mandatory 3 4492.8 499.2 Optional high band 4 6489.6499.2 Optional 5 6988.8 499.2 Optional 6 7488.0 499.2 Optional 7 7987.2499.2 Mandatory 8 8486.4 499.2 Optional 9 8985.6 499.2 Optional 109484.8 499.2 Optional 11 9984.0 499.2 Optional

The PHY narrowband can include the following:

Scrambler→Channel coding [BCH (n=63, k=51)]→Pad bits→Spreader→Bitinterleaver

TABLE 5 Impulse Radio (IR), On-Off signaling Uncoded bit rate (Mbps) FECrate Coded bit rate (kbps) 0.487 0.81 394.8 0.975 0.81 789.7 1.950 0.811,579.0 3.900 0.81 3,159.0 7.800 0.81 6,318.0 15.600 0.81 12,636.0

TABLE 6 Impulse Radio (IR), DBPSK/DQPSK modulations Uncoded bit rateCoded bit rate Mod (Mbps) FEC rate (kbps) DBPSK 0.487 0.5 243.0 DBPSK0.975 0.5 457.0 DBPSK 1.950 0.5 975.0 DBPSK 3.900 0.5 1,950.0 DBPSK7.800 0.5 3,900.0 DBPSK 15.600 0.5 7,800.0 DBPSK 0.557 0.5 278.0 DQPSK1.114 0.5 557.0

TABLE 7 FM (optional), FM-UWB data rate Uncoiled bit rate (Mbps) FECrate Coded bit rate (kbps) 250 0.81 202.5

The PHY human body communications specification is for human bodycommunications (HBC) physical layer (PHY) that uses the electric fieldcommunication (EFC) technology. The electrode in contact with the bodyis used for transmitting or receiving an electrical signal through thebody to a device (e.g., smartphone). The band of operation can becentered at about 21 MHz. FIG. 11 illustrates the PHY human bodycommunications.

In an embodiment, within the medical implant communication service, afrequency of about 402 MHz to about 405 MHz can be allocated (per theFCC), as this range can provide reasonable signal propagationcharacteristics in the human body.

TABLE 8 Frequency data for medical implant communication service.Frequency Band Number of Channel Typical Data (MHz) Channels BandwidthRates 402-405 10 300 KHz 75.9-455.4 Kbps

In this case, a short-range, wireless link may be desired to connectlow-power implanted medical devices with monitoring and controlequipment. Implanted medical devices include, but are not limited to,cardiac pacemakers, implantable cardioverter/defibrillator (ICD),neuro-stimulators, etc.

As the foregoing data illustrates in terms of the current invention,certain embodiments address the need for higher data ratecommunications. Currently, with conventional technologies, traditionalimplants use inductive links, have a limited range (in contact withpatient), have low frequency (data rates similar to a dial-up computermodem), and low data rate communications in the MICS band (75.9-455.4Kbps). Using certain embodiments of the current invention, however,provide higher data rates, upload patient events captured in the IMD'smemory to the base station for analysis, and shorten doctor-patientconsultancy times.

In Vivo Wireless Channel Characterization and Signal Processing

Software can be utilized to simulate the RF channel. Such simulationsare key to providing general results and intuition before experimentallysounding channels. The experimental channel sounding, with phantoms andlive models, can then provide raw data samples of the in vivo channelitself and lead to useful datasets. More useful are parametric modelsthat can iteratively evolve based on the simulations and experimentalmeasurements. Such models improve the ability to pursue endeavors in thebiomedical device field specifically with regards to wirelesscommunications from in vivo devices. Given data from simulated,measured, and modeled channels, a thorough analysis includesbenefit/cost behavior of implanted devices, performance as a location ofdevices in the body, power consumption, and degree of invasiveness. Oncepoint-to-point communications are well understood, the possibilities ofnetworking in vivo nodes can be examined. The modality/scenariocombinations can then be tested in phantoms and live models (porcinesubjects) to determine effectiveness.

Well-studied wireless environments include, for example, cellular, WLAN,and deep-space. Because of near-field effects (at low operatingfrequencies) and multi-path scattering (at high operating frequencies)with propagation through different types of human organs and internalstructures between closely spaced transmitter and receiver antennas,characterizing in vivo wireless propagation facilitates optimization ofcommunications and requires familiarity with both the engineering andthe biological environments.

Free Space and In Vivo Attenuation

Simulated attenuation in HFSS was achieved, where a signal travels froma monopole placed inside the abdomen to an external monopole with a 30cm transmission path (9 cm of the path are inside the body). Antennaeffects have been removed in software by simultaneously matching eachantenna port impedance in Agilent ADS. Signal loss can be seen in FIG.12 for in vivo attenuation and free space loss. As can be seen,attenuation drop-off rate is not constant and is seen to increase morerapidly above 2.2 GHz.

In Vivo Attenuation and Dispersion

To test in vivo attenuation and dispersion, the carrier frequency wasabout 1.2 GHz and the video signal bandwidth was 5 MHz. The FMmodulation bandwidth was about 11 MHz. The transmitter was locatedinside the abdominal cavity. The receiver was placed about 0.5 m fromthe transmitter in front of the abdomen. In FIGS. 13A-13B, it can beseen that there is about a 30 dB difference in signal strength betweenthe in vivo and the external measurement, which shows that there isapproximately 30 dB of attenuation through the organic tissue. Thisseems to be in good agreement in what is shown in FIG. 12. In vivo timedispersion is much greater than expected from the physical dimensions.

In Vivo Wireless Channel Directional Properties

One of the many differences between classic RF models and the in vivochannel is that the path loss and impulse response is a function of thedirection (receiver location). As seen in FIGS. 14A-14B, the path lossis a function of the frequency and not homogenous around the body.Moreover, the angular dependency is noticeable for 500 MHz. The distancebetween transmitter and receiver is 30 cm with center frequencies of 2GHz (side body), 1 GHz (front body), and 0.5 GHz (back body).

MIMO In Vivo

A multiple-input and multiple-output system is contemplated for in vivocommunications. In particular, multiple transmit and receive “smart”antennas can increase wireless capacity. As seen in FIG. 15A, amultipath scattering scrambles the signals, each receiver having adifferent combination of signals. A digital signal processing algorithmde-scrambles the received signal to reproduce the original signals anddeliver the energy to the target receiver. As seen in FIG. 15B, capacityincreases about linearly with the number of antennas with no increase intotal power.

MIMO techniques, such as the schematic seen in FIG. 16, may be used tointerrogate power-limited, or passive, sensors. If feasible, this couldhave the potential dual benefit of not only enhancing the data ratespossible through spatial multiplexing. Advantages can include, forexample, increased read reliability using spatial diversity, increasedread range and throughput, no increase in power consumption with higherdata rate, and full channel information at the reader through sensorbackscatter. A contemplated application of this technique is RFID forpassive devices.

Network Coding

Network coding (NC), as indicated in FIG. 17, achieves capacity gainthrough coding of information, making reliable networks/systems out ofrelatively unreliable subsystems. NC improves network reliabilityagainst packet losses and link failures (and coding provides somesecurity against casual or malicious listeners/intruders) bytransmitting different forms data down multiple paths, such that even ifone or more paths fail to deliver their information, the data stillreaches the recipient which can deduce the data.

Wireless Miniature Anchored Robotic Videoscope for Expedited Laparoscopy(MARVEL) Camera Module (CM)

The MARVEL system is a wirelessly controlled and communicatinghigh-definition video system that provides the spatial and visualadvantages of open-cavity surgeries. As seen in FIG. 18, the MARVELsystem included (1) multiple CMs with wirelessly controlled pan/tiltenabling a full hemisphere field of view inside the abdominal cavity,wirelessly adjustable focus, and a multi-wavelength illumination controlsystem; a Master Control Module (MCM) that provides a near-zero latencyvideo wireless communications, independent wireless control for multipleMARVEL CMs, digital zoom; and a wireless human-machine interface (HMI)that controls the CM functions. U.S. Pat. No. 8,416,342 furtherdescribes imaging devices of this nature and is incorporated herein byreference in its entirety.

The MARVEL CM is an example of one device that can be used in a familyof wirelessly networked in vivo biosensors and actuators that arecapable of wirelessly communicating to one or more external nodes. Byaccomplishing this, the system has particular advantages and benefitsincluding, but not limited to, decreasing the surgical-tool bottleneckexperienced by surgeons in laparo-endoscopic single-site surgicalprocedures; eliminating power, video, and light source cabling issues incurrent laparoscopes; increasing the dexterity and fine motion optionsfor the surgeon; and increasing the imaging angle and the usableworkspace inside the abdominal cavity.

All referenced publications are incorporated herein by reference intheir entirety. Furthermore, where a definition or use of a term in areference, which is incorporated by reference herein, is inconsistent orcontrary to the definition of that term provided herein, the definitionof that term provided herein applies and the definition of that term inthe reference does not apply.

The advantages set forth above, and those made apparent from theforegoing description, are efficiently attained. Since certain changesmay be made in the above construction without departing from the scopeof the invention, it is intended that all matters contained in theforegoing description or shown in the accompanying drawings shall beinterpreted as illustrative and not in a limiting sense.

It is also to be understood that the following claims are intended tocover all of the generic and specific features of the invention hereindescribed, and all statements of the scope of the invention which, as amatter of language, might be said to fall therebetween.

What is claimed is:
 1. A system for performing networked medicalprocedures on a subject, comprising: a plurality of in vivo medicaldevices, said plurality of in vivo medical devices including an in vivotransmitter that is positioned to maximize bit-error-rate; a networkproviding a communication path between a first in vivo medical deviceand a second in vivo medical device each selected from the plurality ofin vivo medical devices, said network comprising a Layer 3 data network,said network permitting said first in vivo medical device to receive afirst control signal and to transmit a second control signal from saidfirst in vivo medical device to said second in vivo medical device oversaid communication path, said communication path including a signalhaving a specific absorption rate less than or equal to 0.08 W/kg; andan ex vivo control unit to control the behavior of the plurality of invivo medical devices, said behavior including physical movement andpositioning of said plurality of in vivo medical devices, saidpositioning of said in vivo transmitter being furthest from organs andtissues within said subject; said network providing a wirelesscommunication path between the control unit and said first in vivomedical device and also between the control unit and said second in vivomedical device, wherein each of the plurality of in vivo medical devicesis separately wirelessly addressable and controllable.
 2. The system ofclaim 1, further comprising: a second wireless communication pathbetween at least one of the plurality of in vivo medical devices and anex vivo system, wherein the second wireless duplex communication path isa duplex communication path.
 3. The system of claim 1, wherein thecontrol unit is a magnet.
 4. The system of claim 1, wherein the controlunit is an electronic device that generates control signals.
 5. Thesystem of claim 1, wherein the control unit is an electronic device thatgenerates communication signals.
 6. The system of claim 1, wherein eachof the plurality of in vivo medical devices are one or more medicaldevices chosen from the group consisting of an imaging device, a sensor,a power source, and a cutting tool.
 7. The system of claim 1, whereinthe communication path between the at least two in vivo medical devicesis wireless.
 8. The system of claim 1, further comprising: a pluralityof wireless communication paths between the control unit and each of theplurality of in vivo medical devices.
 9. The system of claim 1, furthercomprising: said ex vivo control unit being an expert system.